(i) Field of the Invention
The present invention relates to a device for in-line surface-hardening of products, intended to feed a unit for preparation of the products, this being downstream of the device, of the type comprising a chamber provided with frigorie transfer means for surface hardening the products and at least one conveyor for introducing the products into the chamber and for extracting them.
(ii) Description of the Related Art
Surface hardening a product is an operation consisting in freezing the surface of at least one of the faces of the product for the purpose of facilitating its subsequent preparation. This technique is used in particular to facilitate the slicing of bars of ham and of pork loins, but is also applicable to other food products which have to undergo cutting, salami, dry sausage, sausages, cheese, fish.
Currently known surface-hardening machines are formed by tunnels, open at one end for introducing the products and at one end for extracting the products, and through which extends a continuously running conveyor for transporting the products. Placed into the tunnel are frigorie transfer means formed, in particular, by means for spraying a cryogenic fluid, for example liquid nitrogen.
The current tunnels operate continuously so that the products enter and leave the tunnel at a constant rate. If an incident occurs at a slicing unit located downstream of the tunnel, requiring the latter to be stopped for a prolonged period, the conveyor in the tunnel is stopped by an operator such that the products remain for a prolonged period inside the tunnel. They are thus cooled for an excessive period such that they are frozen too much, in particular frozen to the core.
Upon restarting the installation, there is a risk of the excessively frozen products leaving the tunnel damaging the cutting blades of the slicing unit.
Similar problems are encountered if the slicing unit is made to operate at a slower rate, for example because of a different setting for the thickness of the slices produced. It is then necessary manually to switch to a new setting of the conveyor's speed of advance, and/or to define a new set point for the frigorie transfer means.
It will be appreciated that a "frigorie" is a negative calorie. The term is used when cold is transferred to an article such as during a food freezing operation by spraying a liquid cryogen on an article.